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“Could criminal behaviour be the first sign of dementia?” the Mail Online asks. A US study found an association between sudden, unusual criminal behaviour, such as shoplifting or urinating in public, and various types of dementia.

The study looked at crimes committed by patients suffering from a number of diseases that damage the brain and cause dementia. It found more than 8% of patients had a history of criminal behaviour that first emerged during their illness.

Patients with Alzheimer’s disease, a common form of dementia – were the least likely to commit crimes, while those with a type of uncommon dementia called frontotemporal dementia (FTD) were the most likely to commit crimes including theft, traffic violations, sexual advances and urinating in public. This has long been recognised as an effect of the disorder, as it typically causes a change in personality and can lead to disinhibition.

This study suggests – but cannot prove – that, in older adults, new criminal behaviour could be a sign of brain damage caused by a dementing disorder.

If you are worried about a relative’s behaviour or changes in personality, it is sensible to seek medical advice.

Where did the story come from?

The study was carried out by researchers from Lund University in Sweden, the University of California, and the University of Notre Dame in Australia.

It was funded by the Hennerlöfska Foundation for Medical Research, The Swedish Society of Medicine and the Trolle-Wachtmeister Foundation for Medical Research in Sweden, and the National Institutes of Health (NIH), the Consortium for Frontotemporal Dementia Research, the Tau Consortium and the Hillblom Aging Network in the US.

The study was published in the peer-reviewed medical journal JAMA Neurology.

The Mail’s coverage was accurate but uncritical. Its photos of someone handcuffed and an angry-looking older person were unnecessary.

What kind of research was this?

This was a retrospective study of patients seen at a memory and ageing centre in the US. It was designed to look at the frequency and type of criminal behaviour that occurred among those diagnosed with a dementing disorder.

Such neurodegenerative diseases can cause brain dysfunction in areas such as judgement, executive function, emotional processing, sexual behaviour, violence and self-awareness, and this can result in antisocial and criminal behaviour.

The crimes committed by people with dementia range from theft, traffic violations and violence to hypersexuality and homicide (but the latter is thought to be rare). The researchers wanted to quantify how often this happens and the extent to which this was the event that led the person to being diagnosed with a form of dementia.

What did the research involve?

Researchers reviewed the medical records of 2,397 patients seen at a US memory and ageing centre between 1999 and 2012. These patients had been diagnosed with a variety of neurodegenerative disorders that can cause dementia.

The researchers screened the patients’ medical notes for specific key words to identify criminal behaviour. Keywords were chosen to represent all the criminal behaviours that have been observed in people with dementia. These included court, arrest, criminal, detain, steal, speeding, violation and violence.

The types of criminal behaviour were then stratified according to the following categories:

driving under the influence (aka drink driving)

hit and run

traffic violations

speeding

insubordination towards legal authorities

sexual advances

loitering

public urination

theft

trespassing

violence (including physical and verbal threats)

Only criminal behaviours that occurred during the patient’s illness were included. The criminal behaviour was considered to be the presenting symptom if the doctor specifically indicated this in the medical record.

Researchers then calculated the frequency of criminal behaviour for the following categories of dementia or dementia-like conditions:

Alzheimer’s disease

frontotemporal dementia

semantic variant of primary progressive aphasia – a type of dementia that effects language and communication, such as speaking, reading and understanding

What were the basic results?

Of the 2,397 patients studied, 204 (8.5%) had a history of criminal behaviour that emerged during their illness.

Of the major diagnostic groups, the following proportions exhibited criminal behaviour:

42 of 545 people (7.7%) with Alzheimer’s disease

64 of 171 people (37.4%) with FTD

24 of 89 people (27.0%) with the semantic variant of primary progressive aphasia

six of 30 people (20%) with Huntington’s disease

nine of 61 people (14.8%) with vascular dementia

Criminal behaviour was one of the symptoms that caused 14% of people to be diagnosed with FTD, compared with 2% of patients with Alzheimer’s disease. Of those diagnosed with FTD, 6.4% were more likely to have exhibited violence in this criminal behaviour compared with 2% of people with Alzheimer’s.

Common types of criminal behaviour in the FTD group included theft, traffic violations, sexual advances, trespassing and public urination. In the Alzheimer’s group, the most common crime was traffic violations, often related to memory loss.

How did the researchers interpret the results?

The researchers point out that new criminal behaviours are associated with specific dementing disorders such as FTD, but not with others.

"The findings from this study suggest that individuals who care for middle-aged and elderly patients need to be vigilant in the diagnosis of degenerative conditions when behaviour begins to deviate from the patient's norm, and work hard to protect these individuals when they end up in legal settings," they concluded.

Conclusion

This study looks at an important issue, but it had several limitations that make the results less reliable:

It used data on criminal behaviour taken from patients’ medical notes rather than relying on official criminal records.

Patients referred to the centre may have had more behavioural problems than those with dementia in the general population.

The study cannot show the criminal behaviour was caused by dementia.

The study had no control group, so cannot compare crime rates among healthy adults with those with dementia.

Dementia can lead to changes in behaviour and, in some people, loss of inhibition and aggression.

However, it’s important that people with dementia are not labelled as potential criminals and it should be noted that most are more of a danger to themselves then others.